1. Field of the Invention
The present invention relates, in general, to devices for the vapor deposition of substances and, in particular, to a new and useful metering device for vacuum deposition apparatus, by which the substance to be evaporated can be fed to the evaporator in portions.
2. Description of the Prior Art
Metering devices are employed in vapor deposition apparatus, for example, for the so-called flash deposition, if, for some reasons, the otherwise usual evaporation from a melt is not advantageous, as in case of vaporizing mixtures of several components having very different vapor pressures, so that the more volatile components evaporate first and a condensate layer is obtained which is inhomogeneous in the direction perpendicular to the plane of the layer. Such devices are further used for supplying the substance in crucible evaporation processes.
It is well known to feed the substance to be evaporated to the evaporator surface in an amount corresponding to the desired thickness of the deposited layer, in which case the respective portion is completely evaporated.
A known wire feed device permits a very accurate metering, however, it has the disadvantage that it can be used only for evaporation of substances which can take the form of a uniform thick and deformable wire. Therefore, this method is limited to specific metals and alloys.
The so-called spiral or helical conveyors, which also are frequently employed in vapor deposition apparatus, permit a continuous supply of granular material, but the graduation according to grain size which occurs is to be taken into account. Further, in spite of keeping the operating voltage constant, the supply velocity in spiral conveyors strongly depends on the level and, consequently, the supply rate cannot be controlled by means of the operating voltage. In addition, in spiral conveyors having a small outlet, there is a risk that the outlet will be blocked by vapor condensates if located close to the evaporator. To avoid this, the material to be evaporated egressing from the spiral conveyor may be directed to the evaporation surface over an inclined trough, which, however, has still the disadvantage that, as an obstacle, it causes a shadow in the vapor stream with the possible result of a non-uniform coating, aside from the fact that the trough also may be blocked by condensates.